Agglutinogens in the blood are proteins existing on the surface of every red blood cell in the body. The kind of agglutinogens present on the red blood cells helps determine the blood type of a person. If a person has blood type A, his red blood cells are studded with agglutinogens A only. If blood type B, the agglutinogens present are only agglutinogens B. If blood type AB, both agglutinogens A and B are present. In blood type O, there are no agglutinogens on the surface of the red blood cells.